The present invention relates to a temperature responsive, pressure operated diaphragm valve assembly for use in association with an automobile internal combustion engine.
As is well known to those skilled in the art, an automobile internal combustion engine employs some diaphragm valve assemblies. Because they are operated by the negative pressure developed in the fuel intake system of the engine, each of these conventional diaphragm valve assemblies is generally of a type comprising a valve housing, a diaphragm member defining at least one working chamber inside the valve housing and communicated to the fuel intake system for the introduction of a negative pressure into the working chamber, a valving element adapted to selectively close and open a passage and rigidly carried by the diaphragm member for displacement together with the diaphragm member, and a biasing spring for urging the diaphragm member in one direction for holding the valving element in either an open position or a closed position.
An example of an application of the conventional diaphragm valve assembly of the construction referred to above is an automobile evaporative emission control system for controlling the emission of fuel vapors, generated from one or both of the fuel tank and the carburetor float chamber, to the atmosphere. In this application, the conventional diaphragm valve assembly serves to allow the introduction of the fuel vapors into the fuel intake system only when the negative pressure developed inside the intake system increases to a value sufficient to overcome the biasing force of the biasing spring inside the working chamber. However, it is fairly well understood that the mere introduction of the fuel vapors into the fuel intake system with no regard paid to the engine operating condition and/or the temperature under which the engine is operated is undesirable. By way of example, if the fuel vapors are introduced into the fuel intake system when the engine reference temperature, either the temperature of the engine or that of a cooling water used to cool the engine, is higher than a predetermined temperature, the air-fuel mixture flowing through the fuel intake system towards one or more combustion chambers will undesirably be enriched to such an extent as to result in emission of a relatively large amount of noxious unburned components of the exhaust gases to the atmosphere.
Another application of the conventional diaphragm valve assembly is an exhaust gas recirculating system for recirculating some of the exhaust gases from the engine exhaust system into the fuel intake system, such as disclosed in the Japanese Utility Model Laid-open Publication No. 53-22920, laid open to public inspection on Feb. 25, 1978, which corresponds to the U.S. Pat. No. 4,090,482, patented on May 23, 1978. According to this Japanese Utility Model Laid-open publication or its counterpart U.S. patent, there is disclosed an exhaust gas recirculating apparatus comprising a vacuum operated EGR valve having a diaphragm which forms a vacuum control chamber on one side of the diaphragm, which chamber is fluid connected to a vacuum port formed in the fuel intake system for transmitting a vacuum signal to the chamber in order to operate the EGR valve for controlling the amount of exhaust gases to be recirculated. The apparatus disclosed therein is further provided with a temperature detecting valve adapted for introducing a limited amount of air through an orifice when the engine is operating under a warm-up condition during which the temperature of the engine is not yet sufficiently increased, so that the amount of the gases recirculated during such an engine operating condition is decreased to some extent.
The temperature detecting valve employed in the Japanese Utility Model Laid-open publication is of a type comprising a cylindrical casing having at one end a temperature sensor, a piston member and a biasing spring for biasing the piston member. The temperature sensor includes a thermally expandable wax material and a push rod adapted to be axially moved according to the expansion and contraction of the thermally expandable wax material, the movement of the push rod being transmitted to the piston member to move the latter against the biasing spring. Depending upon the position of the piston member, a communication passage between the orifice and the atmosphere is selectively opened and closed. This temperature detecting valve is an integral valve completely separate from each of the vacuum operated EGR valve and the pressure control valve for controlling the pressure in the recirculating passage to a constant value according to the magnitude of the negative pressure.
The use of the diaphragm valve assembly in the EGR system is also disclosed in the Japanese Utility Model Laid-open Publication No. 53-143921, laid open to public inspection on Nov. 3, 1978. According to this publication, there is employed a diaphragm valve assembly of a type comprising a valve housing having a diaphragm member cooperative with the valve housing to define a working chamber, a biasing spring urging the diaphragm member in one direction, and an elongated valving element having one end connected to the diaphragm member and the other end adapted to selectively close and open the exhaust gas recirculating passage. While the diaphragm member is normally biased by the spring to cause the valving element to close the recirculating passage, the diaphragm member is displaced in the other direction against the biasing spring when the negative pressure introduced into the working chamber overcomes the biasing force of the spring. In this arrangement, a signal transmitting passage extending between a portion of the fuel intake system in the proximity of the throttle valve and the working chamber of the diaphragm valve assembly has a temperature responsive control valve installed thereon. This temperature responsive control valve is so designed as to introduce a regulated amount of air into the signal transmitting passage to reduce the negative pressure flowing therethrough, according to a change in temperature of a cooling water or lubricating oil which takes place in correspondence with the progress of the warm-up of the automobile engine. In this arrangement, the diaphragm valve assembly and the temperature responsive control valve assembly are separate assemblies.
Both of the apparatuses disclosed respectively in the above mentioned Japanese Utility Model Laid-open publications involve the common disadvantage that, since the vacuum signal transmitting passage extending between the fuel intake system and the EGR valve is adapted to be communicated to the atmosphere when the temperature of the engine is relatively low, the negative pressure to be introduced into the working chamber of the EGR valve when the engine remains at a constant temperature tends to fluctuate according to the opening of the throttle valve.